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It is frequently necessary to quickly and accurately determine the statistical characteristics of concrete homogeneity from a few test results. This paper proposes an approximate method for determining c v together with Ray and o, for a given numerical series consisting of n partial strength values Ri, as a function of the minimum Rmi n and maximum Rmax strengths in the series.The method is based on V. V. Stoi'nikov's proposition that "The homogeneity characteristic of concrete in a structure can be considered as the generalized characteristic of the quality of organization and mechanization of the overall process of manufacture, transport, placing and curing of the concrete and control on the particular construction.* For conditions of constant industrial process, for obtaining the basic materials (governing their homogeneity), Ixeparation, transport and placing of the concrete mix, in addition to the concrete curingtechnology, the proposition is justified that the statistical characteristics of homogeneity are a function of the difference between the maximum and minimum stxength of the concrete.

The dam of the Kirovskoe reservoir was constructed in 1971-1975 on the Talas River. The main purpose of the reservoir is for irrigation; its total volume is 550 million m ~, the useful volume 540 million m s. The reservoir was created by a concrete buttress dam, A dam of such type was constructed for the first time in the USSR. The height of the dam is 84 m, crest length 260 m, slope of the upstream and downstream faces 0~With respect to design, the Kirovskoe dam was divided into three zones dependlnE on the working conditions of the concrete in the operating period and was constructed by the "Toktogul" method with the use of sectlonalizatlon into concreting blocks. The widths of the concreting blocks varied from 22 m (head) to 12 m (buttress); the length reached 77 m.Two grades of concrete were used: 25 MPa R18 V-8 Mrz200 (279,000 m ~) and 20 MPa RI6 V-6 Mrz150 (50,000 ms). Concrete grade 20 MPa was placed in the buttresses and downstream heads of the sections.Cements of various grades from different cement plants were used in the initial period of constructin E the dam. Beginning in April 1972 only low-heat sulfate-resistant portland cement grade 300 was used. This simplified the selection and correction of the concrete compositions and promoted an increase of the homogeneit7 of its properties. The cement met all requirements of the technical specifications for cement for constructing the dam of the Kirovskoe reservoir. It main properties were sufficienLly stable, which is characterized by comparatively low coefficients of variation of aotivit~ (C V of compressive strength, 6.1%; Cvof beindinE tensile strength, 12.3Z), specific surface (CV ffi 8.7), and content of alkalies (Cv = 14.0%).

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The necessity frequently arises during the construction of large hydraulic structures to transport concrete ag= gregates over long distances. The quality of these materials and of the mixed concrete depends on a well=thoughtout method of transport from the source of the material to the place of use.The sand=gravel quarry at the construction site of the Krasnoyarsk hydroelectric plant is 70 km downstream of the dam. The gravel screening plant ( Fig. 1) is located at the quarry. The plant has an output of 600 tons/h of screened gravel (washed in summer) in four sizes: 0=5, 5=20, 20=40, and 40=80 mm.The gravel is discharged into intake hoppers. Aggregates of different sizes are delivered by conveyors from a height reaching 15 m to aggregate storage cones 9.. An underground shaft 3 with two conveyor lines is used for the delivery of materials to wharves for loading into barges. Additionally, the material may be delivered by the con= veyors to stock piles in standby storage 4, and further along shaft 5, beneath the stockpiles, to wharves 6. 9 In summer the aggregates are conveyed in barges. The barges are unloaded by means of gantry-cran e clam= shells to handling storage 7 (at the wharf), then through shaft 8 the aggregates are carried by conveyors into pile= stackers of main storage 9, and the aggregates are stockpiled to a height of 10 m. The materials drop from a height of 5 to 10 m into the barges during loading operations. The aggregates are delivered from the main storage through underground shafts 10 and 11 to delivery bins 12 of the concrete mixing plant, where the material is stockpiled to a height of 10 m. From the batching bins the aggregates are transported by conveyors to delivery bins 13 of the concrete mixing plant, and further, through hatching conveyor 14 to the continuous concrete mixer. Thus, the mated= al, while moving from the screening facility to the concrete plant is dumped 6 to 7 times into high heaps of coni= cal shape. When moving along the conveyors the material is handled 28 to 46 times with a total length of conveyor lines of 4714 to 4980 m.